1. Field of the Invention
The present invention relates to a heavy duty pneumatic tire to be attached to a heavy load vehicle such as trucks and buses. More particularly, the present invention relates to a pneumatic tire whose carcass has a radial structure.
2. Description of the Related Art
Heavy duty tires having a radial structure are known. JP-A No. 2-141309 has disclosed a heavy duty tire having a belt ply including a cord which extends in a circumferential direction. U.S. Pat. No. 6,082,425 (JP-A No. 2000-504655) has disclosed a heavy duty radial tire having a belt ply including a cord which extends in a circumferential direction and a belt ply with a bias structure. U.S. Pat. No. 6,401,778 (JP-A No. 2001-522748) has disclosed a heavy duty radial tire having a belt ply including a cord which extends in a circumferential direction and a belt ply with a bias structure.
Dimensions of a tire are enlarged gradually according to mileage of the car. By this enlargement, a tread profile is deformed. The deformation causes uneven wear of the tread. The deformation may cause cracks at a bottom part of a groove formed on the tread. In heavy duty tires having a radial structure and a small aspect ratio, uneven wear and cracks are caused significantly.
In tires with enlarged dimensions, contact pressure on a shoulder part is great. While running, frictional heat is generated resulting from the great contact pressure. By the frictional heat, a belt ply may be separated at the end of the ply. The enlargement of dimensions deteriorates durability of tires.
The object of the present invention is to provide a heavy duty pneumatic tire in which excellent quality can be maintained for a long term.